Tendinopathies are chronic tendon disorders characterized by pain, swelling, and impaired function, typically resulting from repetitive mechanical loading (Millar et al., 2021). Unlike acute tendon injuries, these conditions involve degenerative changes in the tendon matrix, including collagen disorganization, increased ground substance, and neovascularization, rather than classic inflammatory responses (Sandrey, 2003). Tendinopathies are highly prevalent in athletic populations; they account for approximately 30-50% of overuse injuries in sports (Florit et al., 2019), affecting both recreational and elite athletes. The Achilles tendon, patellar tendon, rotator cuff tendons, and lateral elbow extensor tendons are most commonly involved (Maffulli et al., 2003), reflecting the repetitive high-load demands of running, jumping, throwing, and racquet sports. For example, Achilles tendinopathy is reported in 8-15% of runners (Munteanu and Barton, 2011), while patellar tendinopathy may affect up to 40% of volleyball players (Lian et al., 2003).

The pathophysiology of tendinopathy is multifactorial (Millar et al., 2021). Mechanical overload - both in magnitude and frequency - is a key trigger for degenerative changes (Magnusson et al., 2010). Central mechanisms include failed healing responses, collagen disorganization, neovascularization, and altered tendon metabolism (Fouda et al., 2017). Neuromuscular and biomechanical factors, such as muscle-tendon imbalances, decreased flexibility, and abnormal load distribution, also contribute to the development and persistence of tendon disorders (Mersmann et al., 2017). The interplay between mechanical stress and cellular response is mediated by mechanotransduction, where tendon cells convert mechanical loading into biochemical signals, promoting collagen synthesis and tendon remodeling (Stańczak, 2024).

Conservative management aims to reduce pain, restore tendon function, and prevent recurrence (Cardoso et al., 2019). Modalities include activity modification, soft tissue therapy, pharmacologic interventions, shockwave therapy, and progressive loading programs (Cardoso et al., 2019). Among these, eccentric exercise (ECC) has gained prominence due to its physiological basis and evidence of clinical efficacy (Camargo et al., 2014; O’Neill et al., 2015). Eccentric exercise involves controlled lengthening of a muscle-tendon unit under load, as opposed to concentric contractions where the muscle shortens (Couppé et al., 2015). It generates higher tendon tension with lower metabolic cost, making it particularly effective for stimulating tendon remodeling while minimizing fatigue (Camargo et al., 2014). Eccentric loading may enhance collagen synthesis, tendon matrix organization, and upregulation of growth factors like IGF-I, facilitating tendon healing (KJaer, 2004).

Protocols such as those described by Alfredson et al. (Alfredson et al., 1998) for Achilles tendinopathy have demonstrated safety and effectiveness, typically involving repeated sets of slow, controlled eccentric contractions, while load and volume are adjusted based on the athlete’s pain response rather than maximal strength testing. Curwin’s method (Curwin and Stanish, 1984) similarly emphasizes pain-guided progression, combining concentric and eccentric movements while performing the eccentric phase at a faster rate, targeting 20-30 repetitions per set with 3 sets of 10 repetitions and adjusting load or speed to maintain a moderate level of discomfort consistent with functional activity. Specific tendon-targeted exercises have been described to optimize loading: for the Achilles, athletes progress from flat-ground calf raises to leaning calf raises and stair-based exercises, incorporating supine calf raises on a leg press machine to modulate load, and anterior step-downs to engage the soleus as a decelerator of tibial motion during dorsiflexion (Lorenz, 2010); for the patellar tendon, leg press, decline squats, and eccentric step-downs are employed, ensuring concentric movements are performed with both legs and the eccentric phase solely with the involved tendon (Lorenz, 2010); for lateral epicondylitis, eccentric wrist extension, eccentric radial deviation, and eccentric supination exercises are performed with passive return to the start position, with progression achieved by increasing lever arm or external load (Lorenz, 2010). Evidence suggests that these interventions are effective in reducing pain, improving function, and supporting return to sport, yet most studies emphasize clinical outcomes rather than detailed methodological reporting, including load prescription, exercise progression, and sport-specific adaptation (Habets and van Cingel, 2015; Chen and Baker, 2021).

Although eccentric exercise is widely used, no scoping review has synthesized both the clinical and methodological aspects of eccentric training interventions in athletes. Athletes have unique performance demands, and tendon loading must be carefully adjusted. Mapping existing evidence can highlight methodological gaps, such as variability in sets, repetitions, load progression, pain monitoring, and reporting of functional outcomes, ultimately guiding standardized, evidence-based protocols for athletic populations. Therefore, a scoping review is warranted to systematically map the existing literature on eccentric training for tendinopathies in athletes, describe the parameters and progression strategies of interventions, and identify gaps in methodological reporting, ultimately informing standardized, evidence-based protocols for athletes. In this way, this scoping review aims to: (i) map existing studies on eccentric training for tendinopathies in athletes; (ii) characterize intervention protocols (load, frequency, volume, progression, pain monitoring); (iii) summarize clinical outcomes and efficacy; (iv) identify harms or adverse effects; and (v) identify methodological gaps and inform recommendations for future research and practice in sports-specific populations.

The protocol for this scoping review was prepared following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. A pre-defined protocol was registered on the Open Science Framework (OSF) platform on August 21, 2025. The registration can be publicly accessed at the following URL: osf.io/q4vy3.

The selection of studies for inclusion in the review was guided by a set of well-defined eligibility criteria based on the Population-Concept-Context (PCC) framework, a standard approach for scoping reviews. No restrictions on language or publication years were applied.

Population: Studies on human participants who are diagnosed with tendinopathy and are identified as athletes (Tier 2 or more in Participants Classification Framework) (McKay et al., 2022). This includes individuals who exercise to improve performance or who participate in organized sports. The definition was broad to include different levels of athleticism based on training volume and competition level, such as competitive athletes and recreational athletes.

Concept: Studies that investigate any form of eccentric training for tendinopathy, regardless of the specific protocol (e.g., heavy slow resistance).

Context: Studies that investigate eccentric training for tendinopathies within the context of athletic training, sports rehabilitation, or recovery protocols. Considered study designs included randomized experimental and controlled studies and non-randomized experimental and controlled studies.

Population: Studies on non-human subjects or on individuals who do not have a diagnosis of tendinopathy or who do not meet the definition of an athlete. This includes those classified as "exercisers" or "physically active practitioners," who primarily engage in physical activity for general health and fitness, typically with a training volume of less than 2.5 hours per week. Studies that focus on individuals with specific physical impairments classified as Paralympic athletes will also be excluded, as their classification system is distinct.

Concept: Studies that do not investigate eccentric training as an intervention for tendinopathy.

Context: Studies that do not investigate eccentric training within the context of athletic training, sports rehabilitation, or recovery protocols. Review articles, case reports, and studies without accessible full texts were excluded, as they do not offer the primary, unbiased data required for systematic analysis.

A search was conducted across multiple electronic databases on August 21, 2025. The databases selected for this review - PubMed, Scopus, and Web of Science - were chosen for their strong relevance to the fields of biomedicine, physical therapy, and allied health. The search covered all records available from each database's inception up to the search date. To enhance the thoroughness of the review, additional literature was located through a supplementary search on Google Scholar, aimed at capturing both peer-reviewed and gray literature; this step was finalized on August 21, 2025. Additionally, a manual review of reference lists from all included studies and related systematic reviews was carried out to identify any further eligible articles not retrieved through database searches. This manual screening was also completed on August 21, 2025.

The search strategy was carefully developed to ensure specificity by combining keywords with controlled vocabulary terms. Customized search strings were created for each database, taking into account the unique syntax and indexing systems of each platform. The search was organized around three main concepts: the target population (athletes), the intervention (eccentric training), and the condition (tendinopathy). This method was designed to capture all relevant studies, regardless of the specific terminology used by the authors.

A broad range of terms and their variants was included to maximize retrieval. Boolean operators (AND/OR) were employed to combine these terms logically, increasing the precision and relevance of the search results.

The finalized search strategy, along with the selected databases and specific terms used, is detailed in Table 1.

The selection of sources of evidence followed a two-stage process. The initial search results were de-duplicated and imported into a review management software (Endnote online). Two independent authors (R.T. and G.O.) then screened the titles and abstracts of all identified records against the established eligibility criteria. At this stage, studies were categorized as "include," "exclude," or "unclear." Any record flagged as "unclear" or "include" by at least one author proceeded to the next stage. In the second stage, the full texts of all selected records were retrieved and assessed for final inclusion by the same two authors. Any discrepancies between the authors' decisions were resolved through a formal consensus meeting, with a third author (K.G.) serving as an arbiter if a consensus could not be reached. This systematic, multi-stage process was designed to minimize the risk of author bias and ensure the final selection of studies was both comprehensive and objective.

Following the study selection process, data were extracted from each included article using a pre-defined data charting form. This form was developed collaboratively by the author’s team and was piloted on a subset of studies (n = 5) to ensure consistency and accuracy before its use. The extraction process was standardized and systematic, ensuring that data collection was consistent regardless of which author was charting the data. The variables extracted from each study included the study design, participant characteristics, type and location of tendinopathy, specifics of the intervention (e.g., protocol, duration, and frequency), outcome measures used, and key findings reported.

In accordance with the objectives of this review, data were extracted across several domains.

Intervention-related variables included the type of eccentric exercise (e.g., decline squat, slow heavy resistance), targeted tendon, load prescription (absolute or relative, such as % of body weight or repetition maximum), frequency (sessions per week), volume (sets, repetitions), duration of intervention (weeks), and overall program length. Progression strategies were charted (e.g., weekly load increments, speed variation, range of motion adjustments, or pain-guided progression criteria). Where reported, pain monitoring strategies were recorded (e.g., allowance of up to 5/10 pain on a numerical rating scale [NRS] during exercise, visual analogue scale [VAS] criteria for progression or modification).

Efficacy outcomes were summarized, including: (i) Pain (e.g., VAS, NRS, or tendon-specific pain scores during activity or at rest); (ii) Function (e.g., Victorian Institute of Sport Assessment [VISA-A, VISA-P, VISA-H], Lower Extremity Functional Scale, Disabilities of the Arm, Shoulder and Hand [DASH]); (iii) Performance and return to sport (e.g., time to return to training or competition, sport-specific performance tests such as hop test, jump height, or strength testing); and (iv) Tendon structure and physiology (where assessed, e.g., ultrasound imaging measures of tendon thickness, Doppler activity, MRI findings, or stiffness using elastography).

Safety outcomes were extracted wherever reported, including: (i) Adverse events (e.g., exacerbation of symptoms, increase in pain beyond baseline, development of compensatory injuries); (ii) Withdrawal or discontinuation of intervention due to pain or intolerance; (iii) Incidence of serious adverse effects (e.g., tendon rupture or significant musculoskeletal injury during intervention).

Methodological and reporting variables included intervention fidelity (e.g., whether supervised or unsupervised), adherence (e.g., reported completion rates of sessions), co-interventions (e.g., adjunct therapies such as shockwave, injections, or stretching), and level of detail in reporting according to exercise intervention.

Although critical appraisal is not mandatory in scoping reviews, it was undertaken in this study to provide greater insight into the methodological quality of the available evidence and to contextualize the strength and limitations of reported findings. Given the diversity of study designs eligible for inclusion (randomized and non-randomized experimental and controlled studies), design-specific risk of bias tools was applied.

Randomized controlled trials (RCTs) were assessed using the Cochrane Risk of Bias 2 (RoB 2) tool (Flemyng et al., 2023). This instrument evaluates risk of bias across five domains: (i) bias arising from the randomization process; (ii) bias due to deviations from intended interventions; (iii) bias due to missing outcome data; (iv) bias in measurement of the outcome; and (v) bias in selection of the reported result. Each domain is rated as low risk, some concerns, or high risk of bias, based on a structured series of signaling questions. These domain-level judgments are then synthesized into an overall risk of bias judgment for each outcome.

Non-randomized intervention studies were assessed using the Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I) tool (Sterne et al., 2016). This instrument evaluates seven domains of bias: (i) bias due to confounding; (ii) bias in selection of participants; (iii) bias in classification of interventions; (iv) bias due to deviations from intended interventions; (v) bias due to missing data; (vi) bias in measurement of outcomes; and (vii) bias in selection of the reported result. Each domain is judged on a scale from low risk, moderate risk, serious risk, critical risk of bias, or no information. As with RoB 2, signaling questions guide the assessment, and judgments across domains are combined to provide an overall risk of bias rating for each study.

Appraisal findings were charted alongside study data to identify trends in methodological quality (e.g., inadequate reporting of progression strategies, limited monitoring of adverse effects, lack of blinding in outcome measurement) and guided the formulation of recommendations for future research.

The charted data were synthesized using both descriptive and visual approaches to provide an overview of eccentric training interventions for tendinopathy in athletes. Study characteristics (e.g., design, population, tendon involved, and context) and intervention features (e.g., load, frequency, volume, progression, pain monitoring) were summarized using frequency counts, and narrative description. Clinical and safety outcomes were grouped into domains (pain, function, performance/return-to-sport, tendon structure/physiology, and adverse events) and summarized to highlight patterns of evidence across different study designs and athletic populations. The results of the critical appraisal were integrated descriptively to contextualize the methodological rigor of included studies and to identify recurrent areas of bias, incomplete reporting, or heterogeneity in outcome measures.

In addition to narrative and tabular synthesis, an evidence gap map was developed to visually display the distribution of evidence across key dimensions, including study design, athlete population (e.g., sport, competition level), tendon site, intervention parameters (e.g., type of eccentric exercise, progression strategy), and outcome domains (pain, function, performance, tendon structure, safety). Data visualization was employed to enhance interpretability and highlight areas of strength and paucity in the evidence base.

The study selection process for this systematic review followed the PRISMA flowchart (Figure 1). Initially, a total of 2812 records were identified through database searches across PubMed (n = 564), Web of Science (n = 858), and Scopus (n = 1390). After removing duplicate records (n = 947), 1865 records remained for screening.

Following the screening process, 1801 records were excluded based on title and abstract review. A total of 64 reports were sought for retrieval. All 64 reports were successfully retrieved and assessed for eligibility. Of these, 33 reports were excluded due to the following reasons: 15 based on population criteria (e.g., no tendinopathy, no athletes), 4 based on concept relevance (e.g., no eccentric training), and 14 based on context criteria (e.g., no control groups, retrospective studies). Ultimately, 31 studies were included in the final scoping review.

Across the included studies focusing on Pattelar tendon (Table 2), Achilles tendon (Table 3), and hamstring tendon (Table 4), the majority of trials focused on participants in their late teens to early thirties, particularly competitive athletes in jumping sports (Visnes et al., 2005; Bahr et al., 2006; Breda et al., 2021). A smaller subset of interventions recruited middle-aged recreational exercisers with chronic symptoms, often with Achilles involvement (Beyer et al., 2015; Habets et al., 2021; Demir Benli et al., 2022). In terms of sex distribution, most studies enrolled predominantly or exclusively male athletes, especially in soccer and volleyball cohorts (Visnes et al., 2005; Langberg et al., 2007; Niering and Muehlbauer, 2023), though some reported a balanced or mixed representation (Stergioulas et al., 2008; Cunha et al., 2012; Demir Benli et al., 2022).

Regarding the sports represented, the most common discipline was volleyball, featured prominently in studies on patellar tendinopathy (Young et al., 2005; Visnes et al., 2005; Biernat et al., 2014; van Ark et al., 2016; Lee et al., 2020), followed by soccer, particularly in Achilles-related trials (Langberg et al., 2007; Malliaras et al., 2013; Niering and Muehlbauer, 2023). Basketball and track & field also appeared frequently as representative jumping or running sports (Cannell et al., 2001; Cunha et al., 2012; Ruffino et al., 2021). With respect to the tendon involved, patellar tendinopathy was the most commonly studied condition in competitive athletes (Bahr et al., 2006; Breda et al., 2021; Ruffino et al., 2021), while Achilles midportion tendinopathy dominated in mixed or recreational cohorts (Alfredson et al., 1998; Rompe et al., 2007; Beyer et al., 2015; Habets et al., 2021). A few studies extended the scope to other regions such as the proximal hamstring tendon (Verma et al., 2022) or quadriceps tendon (Visnes et al., 2005).

The eccentric training protocols (Table 5) described across the studies showed considerable heterogeneity. Bodyweight decline squats performed on a 25° board were the most common exercise strategy for patellar tendinopathy (Young et al., 2005; Visnes et al., 2005; Jonsson and Alfredson, 2005; Bahr et al., 2006; Breda et al., 2021). For Achilles tendinopathy, the Alfredson heel-drop program - consisting of eccentric calf raises with the gastrocnemius and soleus (straight and bent-knee variations) - was the most widely used (Alfredson et al., 1998; Knobloch et al., 2007; 2008; Rompe et al., 2007; 2009; Habets et al., 2021). These core protocols were often modified with additional resistance (typically backpack weights with incremental loading of 5-10 kg) or adapted with alternative devices, such as barbell-guided squats (Frohm et al., 2007), inertial flywheels (Ruffino et al., 2021), or adjunctive modalities like AirHeel wraps (Knobloch et al., 2007; 2008). In some studies, eccentric protocols were paired with comparators such as shockwave therapy (Rompe et al., 2007, 2009; Demir Benli et al., 2022), laser therapy (Stergioulas et al., 2008), or high-load slow resistance (Beyer et al., 2015; Ruffino et al., 2021).

Training frequency was consistently high, with the majority prescribing two daily sessions, 7 days per week following the Alfredson or decline squat model (Alfredson et al., 1998; Visnes et al., 2005; Jonsson and Alfredson, 2005; Bahr et al., 2006). Alternative approaches reduced frequency to 3 sessions per week in heavy slow resistance programs (Beyer et al., 2015; Ruffino et al., 2021) or supervised gym-based regimens (Cannell et al., 2001; van Ark et al., 2016). Training volumes typically amounted to 3 sets of 15 repetitions per exercise, leading to ~90 reps/day in most eccentric-only models, while heavy resistance protocols varied intensity through progressive loading based on percentage of 1RM (repetition maximum) or RM ranges (15RM → 6RM) (Malliaras et al., 2013; Ruffino et al., 2021). Pain monitoring was an integral feature of nearly all protocols, with eccentric programs generally allowing participants to exercise into moderate pain (VAS 4-5/10) as part of progression (Visnes et al., 2005; Jonsson and Alfredson, 2005; Bahr et al., 2006), whereas comparator protocols (e.g., isotonic or isometric training) emphasized pain minimization (VAS <3/10) (van Ark et al., 2016; Sánchez-Gómez et al., 2022).

Across the 29 randomized trials (Table 6), the most frequent source of bias was lack of blinding of participants and reliance on self-reported outcomes such as VISA-P/VISA-A and pain scores. In nearly all studies, interventions were obvious - e.g., eccentric decline squats (Jonsson and Alfredson, 2005; Visnes et al., 2005), heavy slow resistance (Kongsgaard et al., 2009; Beyer et al., 2015), extracorporeal shockwave therapy (Rompe et al., 2007; Rompe et al., 2009), and adjuvant modalities like low-level laser (Stergioulas et al., 2008) - making patient blinding impossible. This inevitably creates “some concerns” in the domains of deviations from intended interventions and measurement of the outcome, since participants’ expectations and therapists’ involvement may have influenced adherence and reporting in many trials (e.g., Bahr et al., 2006; Abat et al., 2016; Lee et al., 2020; Habets et al., 2021; Ruffino et al., 2021). A rare counter-example was Malliaras et al. (2013), which achieved low risk across all domains.

Another common issue was selective reporting and trial registration, especially in older studies. Several trials conducted before 2010, such as Visnes et al. (2005), Jonsson and Alfredson (2005), and Knobloch et al. (2007), had no preregistration and limited outcome justification, resulting in some concerns or high risk in the “selection of reported results” domain. Conversely, modern trials like Demir Benli et al. (2022) and Knež and Hudetz (2023) reported robust randomization, balanced attrition, and registration, leaving only performance/measurement bias as residual concerns.

Both non-randomized studies (Table 7) were judged to be at serious overall risk of bias. In Alfredson et al. (1998) concerns arose from reliance on unblinded self-reported outcomes, placing outcome measurement at serious risk of bias. In Gómez et al. (2023), although objective measures such as echography and performance tests were included, the small sample size, absence of blinding, and concurrent athletic participation contributed to moderate to serious concerns. Across both studies, selective reporting could not be excluded due to the absence of preregistered protocols.

Across patellar tendinopathy studies (Table 8), eccentric loading consistently reduced pain and improved function (Jonsson and Alfredson, 2005; Knež and Hudetz, 2023), with HSR providing comparable or superior long-term outcomes (Kongsgaard et al., 2009; Ruffino et al., 2021). Adjunctive modalities such as US-guided galvanic electrolysis, ESWT, or supplementation accelerated early symptom relief in some cases - typically within the first 4-6 weeks (up to 8 weeks in some protocols) - although in-season interventions often showed limited short-term functional gain, with no meaningful improvements across the 0-12-week competitive-season period (Abat et al., 2016; Lee et al., 2020; Sánchez-Gómez et al., 2022; Visnes et al., 2005). Most programs demonstrated high return-to-sport (RTS) rates (Cannell et al., 2001; Bahr et al., 2006), while performance improvements were variable (Biernat et al., 2014; Niering and Muehlbauer, 2023). Structural responses favored high-load resistance with reduced neovascularization and enhanced tendon quality (Kongsgaard et al., 2009), though remodeling was inconsistent in other protocols (Lee et al., 2020). Overall, exercise-based care was safe and well tolerated, with occasional discomfort and low dropout except when using concentric-only loading (Jonsson and Alfredson, 2005).

For Achilles tendinopathy (Table 9), eccentric approaches demonstrated consistent analgesic and functional benefits across populations (Alfredson et al., 1998; Habets et al., 2021), while HSR achieved similar or sometimes superior long-term results (Beyer et al., 2015). Adjuncts such as ESWT and laser therapy were effective when combined with exercise but showed less uniform benefits alone (Stergioulas et al., 2008; Rompe et al., 2009). Return-to-activity outcomes were strong (Alfredson et al., 1998) and comparable to surgical interventions without the associated risk profile (Bahr et al., 2006). High-load protocols led to the greatest structural and physiological adaptations, including improved collagen turnover and stiffness (Langberg et al., 2007; Radovanović et al., 2022), while bracing improved microcirculation (Knobloch et al., 2007, 2008). Across studies, interventions were safe, with transient soreness the most common adverse effect.

Evidence for proximal hamstring tendinopathy remains sparse (Table 10), but a combined protocol using high-power laser therapy with exercise demonstrated significant short-term reductions in pain and gains in strength in track-and-field athletes, with no reported complications (Verma et al., 2022). While early responses are promising, the lack of long-term and structural data limits definitive conclusions for this tendon site.

To provide a visual overview of the research landscape, three evidence gap maps were constructed (Figure 2, Figure 3 and Figure 4). Figure 2 shows the distribution of studies by tendon site and sport type. The majority of evidence focuses on patellar tendinopathy in volleyball and basketball athletes and Achilles tendinopathy in running-related sports. Only a single study addressed proximal hamstring tendinopathy in track and field athletes (Verma et al., 2022), highlighting a clear evidence gap.

Figure 3 summarizes tendon site versus outcome domains. Pain and function are the most consistently reported outcomes across both patellar and Achilles tendinopathy. In contrast, performance/return-to-sport and tendon structural/physiological adaptations are less frequently measured. Safety and adverse events were systematically reported in fewer studies, often limited to minor soreness or calf ache, indicating under-reporting of potential harms.

Figure 4 illustrates intervention type versus outcome domains. The majority of trials investigated eccentric-only protocols, while eccentric exercise combined with adjuncts such as heavy slow resistance, shockwave therapy, laser therapy, or electrolysis have become increasingly frequent. Multimodal rehabilitation programs remain less explored but tended to include structural and performance outcomes beyond pain and function.

This scoping review synthesized evidence from 31 studies investigating eccentric training (ECC) for tendinopathies in athletic populations, spanning patellar, Achilles, and proximal hamstring tendinopathies, with most interventions involving competitive or elite athletes in volleyball, basketball, soccer, and track and field. While the majority were randomized controlled trials, sample sizes were often modest and protocols varied markedly in load progression, dosing frequency, and pain monitoring strategies. Comparator interventions ranged from surgery and heavy slow resistance (HSR) to shockwave therapy (ESWT), laser, or conservative physiotherapy, highlighting a broad translational context but complicating direct synthesis. Across outcomes, ECC consistently demonstrated reductions in pain and improvements in tendon-related function, with more heterogeneous findings for return-to-sport (RTS), athletic performance, and tendon structural remodeling. Adverse effects were infrequent and mild. Nevertheless, uncertainties remain regarding long-term durability, sport-specific reintegration, and standardized safety tracking.

Evidence for patellar tendinopathy overwhelmingly supports eccentric loading as an effective intervention for reducing pain and improving tendon-related function in athletes, with clinically meaningful VISA-P gains reported in nearly all trials, including improvements from approximately 30-55 to 70-90 points within 12-24 weeks (Abat et al., 2016; Frohm et al., 2007; Breda et al., 2021; Knež and Hudetz, 2023). When compared directly with alternative exercise or conventional rehabilitation, eccentric training was consistently superior or equivalent, and greatly outperformed concentric training, which showed minimal improvement and poor tolerance (Jonsson and Alfredson, 2005). Multimodal or progressive loading programs such as progressive tendon-loading exercise revealed advantages over traditional eccentric exercise in reducing pain during tendon-loading tasks and promoting improvements in load tolerance, movement quality, lower-limb strength, and the ability to perform sport-specific tasks without symptom escalation (Breda et al., 2021). Performance outcomes were less consistent: some interventions increased jump performance, change-of-direction speed, and lower-limb strength (Frohm et al., 2007; Sánchez-Gómez et al., 2022; Niering and Muehlbauer, 2023), while others showed only small or nonsignificant changes despite clear clinical gains (Biernat et al., 2014). RTS was infrequently reported but generally favorable when included, with 67-90% return to sport by 12 weeks in studies using structured decline protocols (Cannell et al., 2001; Jonsson and Alfredson, 2005). Structural adaptations varied: high-load and injection-comparison studies revealed reductions in tendon neovascularity and improved collagen turnover (Kongsgaard et al., 2009), while others found symptomatic relief without remodeling (Lee et al., 2020), suggesting a potential disconnect between symptom change and tissue response. Importantly, adherence influenced outcomes -low compliance in some in-season studies may explain the absence of improvement (Visnes et al., 2005). Across the body of evidence, safety was strong, with no serious adverse events and withdrawals primarily linked to poorly tolerated concentric loading. These findings endorse eccentric and progressive tendon-loading programs as an effective cornerstone rehabilitation strategy in athletic patellar tendinopathy, particularly when external load is adequately progressed and adherence is supported.

Midportion Achilles tendinopathy research demonstrated highly consistent pain relief and VISA-A improvements with eccentric heel-drop protocols across recreational and competitive athletes, with typical improvements of 30-40 VISA-A points over 12 weeks (Alfredson et al., 1998; Habets et al., 2021; Rompe et al., 2007). Although ESWT and other adjuncts yielded short-term benefits when combined with exercise (Rompe et al., 2009; Stergioulas et al., 2008), ECC and HSR produced greater or more durable clinical change, with the latter showing the highest patient satisfaction and adherence (Beyer et al., 2015; Radovanović et al., 2022). Return-to-sport outcomes were favorable where reported - Alfredson et al. (1998) demonstrated 100% return to running by 12 weeks - yet most trials failed to track long-term RTS consistency or match recovery timelines to competitive calendars. Performance capacity was seldom evaluated, though selective studies noted strength or maximum voluntary contraction improvements with high-load protocols (Radovanović et al., 2022). Tendon structure and physiology responses differed by loading strategy: conventional ECC improved symptoms more than morphology, while high-load training demonstrated superior improvements in tendon stiffness, collagen turnover markers, and cross-sectional area, aligning with a mechanotransduction-driven restoration of tendon capacity (Langberg et al., 2007; Radovanović et al., 2022; Malliaras et al., 2013). Importantly, ESWT alone did not significantly alter tendon structure despite reducing symptoms (Rompe et al., 2007), underlining that structural recovery is load-dependent. Adherence remained high across studies, and adverse effects were minimal, typically limited to transient soreness. The Achilles literature therefore presents a mature evidence base supporting ECC and progressive loading strategies for pain and function, while highlighting critical ongoing gaps in performance return, season-specific rehabilitation design, and long-term tendon health monitoring.

The evidence for proximal hamstring tendinopathy in athletes is notably sparse, with only one included controlled trial meeting criteria. The findings suggest that an eccentric-informed protocol integrating high-power laser therapy promotes meaningful reductions in pain and improvements in hamstring strength, while the comparator program produced more modest change (Verma et al., 2022). Although these outcomes indicate that tendon loading can be beneficial for PHT, the trial did not evaluate VISA-style function metrics, jump or performance outcomes, RTS, or tendon structural adaptation, limiting interpretation. Moreover, follow-up did not extend beyond the short post-intervention phase, and sample size was small with no imaging verification of tendon change. Given the high recurrence risk and major performance implications of PHT in sprinting and change-of-direction sports, the lack of robust evidence represents a concerning gap. High-quality randomized trials including season-specific outcomes and tendon capacity measures are urgently required.

The heterogeneity of ECC prescriptions - spanning frequency, external load, progression rules, and pain-monitoring - hinders the ability to define optimal dosing for athletes. Outcome reporting prioritized pain and VISA measures, while RTS measures, tendon remodeling, and performance capacity were inconsistently collected despite their importance for athletic return and reinjury prevention. Most studies enrolled young male athletes, limiting generalization to female athletes, older competitors, or athletes in endurance or collision sports. Methodological limitations included limited blinding, short follow-up, inadequate adherence reporting, and insufficient monitoring for adverse events and reinjury. Research should prioritize long-term, sport-focused RCTs with clear RTS criteria, sex-balanced recruitment, and standardized tendon-loading parameters. Improved reporting of structural adaptation, intervention fidelity, safety, and athletic performance is needed. Comparative and multimodal studies may clarify optimal loading strategies and personalization of tendon rehabilitation in high-performance sport.

Despite the limitations, ECC remains a safe, accessible, and effective first-line treatment for patellar and Achilles tendinopathy in athletes, improving pain and function without interrupting participation for many cases. High-load resistance strategies (e.g., HSR) may enhance long-term outcomes and tendon mechanical properties. However, clinicians should supplement ECC with comprehensive RTS assessment, address sport-specific load demands, and tailor pain exposure and progression individually. Objective monitoring of performance and tendon health may help optimize rehabilitation and reduce recurrence risk. For under-studied tendon sites such as proximal hamstrings, evidence-based protocols cannot yet be standardized.

This scoping review shows that most research on eccentric training in athletes has concentrated on patellar tendinopathy (particularly in volleyball and basketball players) and Achilles tendinopathy (especially in running and soccer populations), with limited attention to other tendon sites. The main outcome domains analyzed were pain reduction, functional improvement, return-to-sport rates, performance outcomes, and tendon structural or physiological adaptations. Findings consistently support pain and functional improvements, with generally favorable return-to-sport outcomes, while evidence for performance enhancement and tendon remodeling remains inconsistent. Reporting on safety outcomes was limited, though adverse events were rare. Significant methodological gaps persist, including heterogeneity in exercise prescriptions, inconsistent progression strategies, and limited long-term follow-up. There is a particular need for standardization of training regimens and parameters - such as load, frequency, volume, and pain-monitoring criteria - to improve comparability across studies. Addressing these gaps with harmonized protocols and comprehensive outcome reporting will be essential for developing evidence-based, sport-specific recommendations for athletes with tendinopathy.